1. Field of the Invention
The present invention relates generally to a mobile camera optical lens system and, more particularly, to a mobile camera optical lens system which assures a wide view angle by dividing an original view angle into a plurality of view angles and provides separate off-axis lens systems corresponding to the split view angles, thereby achieving a thinner mobile camera optical lens system.
2. Description of the Related Art
Recently, with the development of digital technology, the improvement of image compression, and the improvement of recovery technology and the peripheral technology of multimedia products, research into accomplishing the thinness and miniaturization of the mobile camera lens is being conducted. In order to meet such a tendency, cameras having high portability on thinner camera lens optical systems as well as excellent performance have been required.
Conventionally, a coaxial camera lens system, in which a plurality of rotation symmetry-type lenses is vertically arranged with respect to the direction of an optical axis, is generally used as an optical system lens for mobile cameras. Such a coaxial camera lens system is illustrated in FIG. 1. Referring to FIG. 1, the coaxial camera lens system generally has a limitation in the reduction of the length thereof in the direction of the optical axis thereof because several rotation symmetry-type lenses are vertically arranged. In particular, since the overall length of the mobile camera lens system is determined to be approximately the same as the diagonal length of an image sensor, there is a problem in that it is very difficult to achieve the miniaturization of a mobile device.
Therefore, in order to resolve such a problem, an optical lens system which achieves the miniaturization of a mobile device using a prism lens, and an optical lens system which achieves the miniaturization of a mobile device using a relay-type off-axis focusing lens, have been proposed.
U.S. Pat. No. 6,084,715 discloses an optical system using a prism lens, the construction of which is described with reference to FIG. 2. It can be seen that the mobile camera optical lens system includes a first prism 10, a second prism 20, a low-pass filter 4 and an image plane 3. However, as illustrated in the drawing, although the mobile camera optical lens system is constructed using a prism lens system, the ratio (overall length/diagonal length of image sensor) of the overall length of the optical system to the diagonal length of an image sensor falls within a range of 2.4 to 4.3, so that there is a limitation in the reduction of the overall length of the optical system.
As another example, Japanese Unexamined Patent Publication No. 2000-292371 discloses an optical system using an off-axis focusing lens, the construction of which is described with reference to FIG. 3. It can be seen that the mobile camera optical system includes a first surface R1, which is a diaphragm, a second surface R2, which is a refracting surface coaxial to the first surface, a third surface R3, which is a reflecting surface inclined with respect to the second surface R2, a fourth surface R4, a fifth surface, which is a reflecting surface shifted and inclined with respect to a corresponding surface, and a sixth surface R6, which is a refracting surface shifted and inclined with respect to the fifth surface R5.
However, even in the case of the integral off-axis focusing lens optical system, the ratio of the overall length of the optical system to the diagonal length of an image sensor (overall length/diagonal length of image sensor) falls within a range of 2.4 to 4.3, as described above. Although there is an advantage in that the length of an optical axis is shorter than that of a conventional coaxial camera lens system, as described above, there are considerable limitations in the achievement of a wide view angle on a single image sensor and, simultaneously, the reduction of the overall thickness of the optical system.
Furthermore, although, in the above-described conventional optical system, a method of reducing the overall thickness of the optical system by decreasing the size of the image sensor can be considered, the method also has few effects in that there is a limitation in the reduction of the size of the image sensor.
As a result, in order to implement a wide view angle using a single image sensor in a mobile camera optical lens system and, simultaneously, reduce the overall thickness of the optical system, an optical lens system, other than the above described lens system using the prism lens and the integral off-axis focusing lens system is required.